Hot Rod Forum banner

Electric Fuel pump wiring?

19K views 46 replies 9 participants last post by  EOD Guy 
#1 ·
Hello, I'm trying to figure out the best way to wire an electric fuel pump for a 1966 Impala.

Most diagrams I saw have them going to the oil pressure switch, however, I'm running mechanical gauges, and I no longer have the oil pressure switch.

Can anyone propose the best, safest option?

Thanks in advance
Shawn
 
#2 ·
The oil pressure switch is there to shut off the pump if the engine quits. There are a number of pressure ports you can tap into to add one to your fuel pump wiring.
I have part numbers at home if you want one. I generally use one from a Vega but any low pressure switch will work.
Mark
 
  • Like
Reactions: mauls
#4 ·
Fuel pump wiring

The switch you looking for is a 12-810 Holley the instructions will show you how to wire it. If the fuel pump is mounted a long way from the battery, I would recommend that you use a (bosh style) 35 amp relay and a fused #10 wire from the battery to the relay and from the relay to The pump. Also make sure you have a good ground.
If you use a relay the holley switch just energizes the relay coil wired this way the pump gets full voltage and the switch see less load will arc the contacts less and last longer.
 
#5 ·
The switch you looking for is a 12-810 Holley the instructions will show you how to wire it. If the fuel pump is mounted a long way from the battery, I would recommend that you use a (bosh style) 35 amp relay and a fused #10 wire from the battery to the relay and from the relay to The pump. Also make sure you have a good ground.
If you use a relay the holley switch just energizes the relay coil wired this way the pump gets full voltage and the switch see less load will arc the contacts less and last longer.
Thanks, but how do I run my oil pressure gauge with this switch? I don't see a way to run both
 
#10 ·
prime

Two things to add.

A gauge type oil pressure switch (sender) is variable resistance that changes with the oil pressure and the warning light type oil pressure switch that closes the circuit when the pressure drops. These are different than a safety shutdown type oil pressure switch that opens the circuit when the pressure drops.

You may want to consider a "prime button" that can be used to run the fuel pump before starting the engine. This is helpful for cars that are stored for extended periods. The fuel in the carb. evaporates over time. This button will run the fuel pump to prime the float bowl.

vicrod
 
#11 ·
Two things to add.

A gauge type oil pressure switch (sender) is variable resistance that changes with the oil pressure and the warning light type oil pressure switch that closes the circuit when the pressure drops. These are different than a safety shutdown type oil pressure switch that opens the circuit when the pressure drops.

You may want to consider a "prime button" that can be used to run the fuel pump before starting the engine. This is helpful for cars that are stored for extended periods. The fuel in the carb. evaporates over time. This button will run the fuel pump to prime the float bowl.

vicrod
I was curious about the car sitting, but then I was thinking if cranking the engine (with empty fuel bowls) would create enough oil pressure for the fuel pump to kick on?
 
#14 ·
I have another question, I just installed the Holley 12-810 oil pressure switch,

Going off the provided diagram it says I wire the N (normally closed) to the starter solenoid.

My question is which terminal does that go to? The R side which goes to the coil, or the S for the starter.

 
#15 · (Edited)
Fuel pump wiring

It goes on the small outside R terminal the small inside terminal S is for the purple
Start wire.
The outside terminal is energized when the solenoid is energized this provides power to the fuel pump( N-C) when cranking once the motor starts and the oil pressure comes up the switch changes poliarty (NO-C) and the power flows from the ignition hot circuit to the fuel pump. :)
 
#16 ·
Fuel pump wiring

The original chevy wiring included a ceramic resistor on the firewall or a resistor in the wire itself to reduce the voltage to the points to make them last longer but it also included a wire from the solenoid R terminal to the coil+ side of the resistor to give the coil+ a full 12V when the solenoid is energized/cranking to help starting. the coil- goes to the points as they ground the coil.

Note this resistor is not used with HEI or other electronic ignitions as they require a full 12V all of the time.
 
#17 ·
Thanks!

This may be hard to troubleshoot on the internet, but I have the strangest issue. For whatever reason the electric fuel pump kicks on only when i turn the headlights on no matter what position the key is in. I'm at a loss right now, according to my wiring nothing ties into the light switch that I've done. I'll provide my diagram below.

Here's the full wiring diagram for a 1966 Chevy Impala



And I use this wiring diagram to wire the fuel pump to the holley oil switch.


In this wiring diagram, I added the electric fuel pump, and oil switch, as well as my wiring.


I wired the NO to the pink wire that goes to the ignition switch. N to the R post on the starter solenoid, and the fuel pump to the C.
I can't for the life of me figure out why it only engages with the headlight switch on, and key switch off.

I know wiring isn't fun to look at so I really appreciate any help you can provide.

Thanks a bunch!
 
#18 ·
IMO........ your NC terminal on the oil safety switch should go to the "S" terminal (purple wire) on the starter not the "I" or "R" terminal (yellow or off-white). As stated above, you only want that wire hot while the vehicle is cranking, while it will work just fine on the "I"/"R" terminal, it just puts another failure point in the fuel pump wiring that isn't needed.

I would remove the NO safety switch terminal from the pink wire and add a fused relay that provides a direct 12 source through the relay and use the pink wire to power the relay. It makes trouble shooting a breeze.

I also added in a bypass switch, that's hooked to the Common side of the safety switch that has no power running to it. I installed a banana female plug to the other side of my bypass switch, and I have a jumper that I keep in the trunk. Been left stranded by a faulty bypass switch twice, now, if I ever get stranded again, I hook up my jumper and bypass all the other stuff
 

Attachments

#20 ·
Fuel pump wiring.



I don't agree with wiring your fuel pump to the S terminal as doing this requires the ignition switch to supply enough amperage to energize the solenoid and run the fuel pump. wireing it to the R post as it will provide plenty of amperage to run the pump. The only reason to utilize a relay is to provide full voltage to the pump in which case you would use the wire from the C to trigger the relay.
 
#19 ·
Fuel pump wiring.

First of all the wiring of the fuel pump switch looks correct to me

The question is why is it back feeding thru the light switch?
Well if we start with your wiring diagram following the orange hot wire from the battery it goes up to a junction where it splits to power The alternator the voltage regulator and the horn relay from there it continues on to a connector at the back of the fuse box (this connector also includes wiring for the headlights and is a potential point where there could be a short circuit) from the fuse box the orange hot wire continues to another junction where it splits to Power the cigarette lighter, the voltage regulator ,the ignition and the headlights. This is where the power is back feeding thru the headlight switch when it's on. So either there is a short at the connector and or the orange hot wire is broke or shorted between the junction and the ignition switch.

So how do you trouble shoot it ? Well first a power probe or a multimeter would be best but if your working under the dash a 12v test light would be easier to use. I would start by checking the hot wire at the ignition switch note the brightness of the bulb then check the ignition terminal with the key on again Note the brightness of the bulb.
And lastly check the start terminal does it crank the motor? If this checks out disconnect / unplug the headlight switch and check them again.

Look for cut bare or burnt or melted wiring this may require you to remove covers or tape but it is necessary. Also look for loose or damaged or corroded connectors at the firewall on motor side. If this car has it's original wiring it's almost 50 years old and god only knows what stereo butchers have done to it .

The last time I ran into phantom wiring like your facing, the previous owner had tried ti install a tape player and melted part of the harness. But I have also seen loose or corroded connectors at the firewall drive people nuts.

Lastly it's possible since it the most used switch in the car,the ignition switch could be bad.
 
#22 · (Edited)
You have your way, and I have mine. My Camaro has been wired this way for many years now with zero issues, except for faulty oil switches.

Running the pump through the fused ign terminal is a lot of amps...... using your logic if the "S" terminal won't handle it I doubt the aux ign terminal will.....
 
#23 ·
Fuel pump wiring

EOD Guy

There are "a lot of ways to skin this cat" and I'm not necessarily saying your method won't work , it will.
But if you get the chance to disassemble and old delco starter solenoid you will find that the switch for the R terminal is a pretty robust and more than capable of handling the amperage of the fuel pump without adding load to the S terminal which operates the coil portion if the solenoid.
There is a reason GM did it this way open one up and it will be apparent.
 
#24 · (Edited)
Fuel pump wiring

EOD Guy

You say that you have had some pressure switch failures I suspect that this could be from running the full amperage for the pump thru the switch.
Every time you use a switch the contacts arc slightly the more amperage the more they arc and this is a regularly used switch.
What I have found is that using a fused (I use circuit breakers) #10 wire from the battery thru a 35 amp rely to the fuel pump provides full voltage to the pump (you can usually hear a difference when the pump is running) the pressure switch is then used to power the coil in the relay which only requires >1 amp which reduces the load and arcing in the pressure switch which should make it last much longer.
Just something to think about.


The reason I suggested taking power for the pump from the fuse block was to get away from the ignition wire which may be high resistance wire to reduce voltage to the points.
 
#25 ·
Thanks for the great info guys!

I removed the ignition switch and tested it with a multimeter and one of the terminals on it is slightly loose, so I'm thinking of replacing that.
Also as you mentioned the wires are very old and brittle. If the ignition switch doesn't fix it, i suspect an exposed or broken wire may be the issue, I'll re-look everything over again.

I will try to remove the light switch and see if I'm still able to crank the car. I'll start here then pursue the other options mentioned above.
I hate wiring and appreciate the help, I know these issues are hard to troubleshoot without being here, but this will give me a great start
 
#26 ·
#27 ·
Greatbaer..... Please don't try and school me on your opinion I have been wrenching for many years........ The faulty switches were due to cheap crappy switches I tried to save a buck on..... nothing else. Bought a quality Holley switch and it's worked just fine for many years.

I'm very familiar with how a starter solenoid/bendix works and what they are made of.

Your statement "The reason I suggested taking power for the pump from the fuse block was to get away from the ignition wire which may be high resistance wire to reduce voltage to the points."

Anybody that takes power from the coil feed wire (I assume that's what you are talking about) and feeds an electric fuel pump needs to hire someone else to do their electrical work.

You are worried the short amount of time that the amperage from the fuel pump will be routed from the purple wire would not run the fuel pump and energize the solenoid at the same time....... don't be ..... it works just fine.

I did not say what you suggested was incorrect........ I just don't do it that way....

Joe, I recently discovered the beauty of the Ford inertia switch and installed one in my Camaro, and plan on including one in any future projects.
 
#28 · (Edited)
I finally got a chance to troubleshoot today and haven't made much progress, but i'm still trying everyone's suggestions.

I removed the light switch, and the car was still able to crank over.

I'm curious If I have the NO on the switch wired correctly? I have it going from the NO on the switch, to the IGN wire on the ignition switch. Is that correct? or should it mate with the purple wire that goes to the Sol on the ignition switch?

I figured i'd start here before I got any further.

Thanks
 
#29 · (Edited)
It's been awhile since I've had the ign switch out but..... I believe the IGN is the feed that powers the coil in the run position either through a ballast resister or a resistance wire.

IMO this circuit was never designed to take on an additional function such as the fuel pump. I would use a feed from it to power a relay, the relay then would power the fuel pump, thus isolating the fuel pump circuit to new heavier gauge wires capable of carrying the load without effecting any of your existing circuits.

The Sol terminal should feed the solenoid on the starter.

The attached diagram is exactly how I have mine currently wired, except the recent addition of a Ford inertia switch.

You connecting the NC terminal on your oil switch to the "S" or "I" terminals on the starter solenoid is irrelevant, both will work
 

Attachments

#30 ·
It's been awhile since I've had the ign switch out but..... I believe the IGN is the feed that powers the coil in the run position either through a ballast resister or a resistance wire.

IMO this circuit was never designed to take on an additional function such as the fuel pump. I would use a feed from it to power a relay, the relay then would power the fuel pump, thus isolating the fuel pump circuit to new heavier gauge wires capable of carrying the load without effecting any of your existing circuits.

The Sol terminal should feed the solenoid on the starter.

You connecting the NC terminal on your oil switch to the "S" or "I" terminals on the starter solenoid is irrelevant, both will work
Alright thanks! So when running the wire to the relay, I should run the relay to the IGN on the starter?

Thanks for dealing with my ignorance, I have no problems building engines, but I am about as green as it gets when it comes to wires. I had the fuel pump running fine when I broke in the engine on the engine run stand, Just when I splice the fuel pump with the car it's a whole new ball game for me.
 
#31 ·
No the relay should be powered by a feed from the ignition switch....pink if I remember right or the "IGN" breakout port/terminal located on your fuse block. The only wire going to the starter would be the NC terminal on the oil switch.

Basically you are using the ign switch to turn on the relay while the key is in the run position, which allows the fuel pump to receive power via the oil safety switch. When the key is in the start position the fuel pump receives power, via the oil switch, from the starter solenoid.
 
#34 ·
Correct, you just need a +12 volt supply with a fuse in it. You could run a new wire from the battery put a 20 amp fuse inline fuse right after the connection from the battery. The purpose..... if that wire shorts the fuse pops and no melt down.

I installed my relay, bypass switch/banana plug along with a remote starter button (protected by a circuit breaker) in an aluminum 2x3 box on my firewall. Makes troubleshooting a breeze.
 
#36 ·
Alright, good news, bad news (i think)

I got the relay switch wired, I haven't done the bypass switch yet, but may do that after i get everything wired and running.

The pump no longer turns on when i turn the headlights on... that's good. Now the pump kicks on when I have the key in the on position. I assume we don't want that, because if we get in a wreck fuel keeps pumping. I'm not sure why the oil switch isn't doing anything, I have 0 oil pressure at the moment, I haven't attempted to start the car yet.

Do you think it's because I have the NC on the oil pump switch going to the R on the starter and not the S?
 
#38 ·
....Do you think it's because I have the NC on the oil pump switch going to the R on the starter and not the S?
I do.

I respectfully disagree with the previous discussion in regards to how it doesn't matter which of the two solenoid terminals you connect to. Sometimes it does matter.

Your car is a case where it does matter, because you have another wire already connected to the 'R' terminal; the wire that connects it to your ignition coil + terminal, whose function is to bypass the ballast resistor and give full battery voltage to the ignition coil while the engine is being started.

I believe what's happening is the fuel pump relay is being triggered by power coming through the 'C' and 'NC' terminals of the oil pressure switch from the starter's 'R' terminal which receives power from it's connection to the ignition coil + anytime the key is on.

Try it on the 'S' terminal and see how it goes. :thumbup:

Good luck...:thumbup:
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top